(1) Technical Field
The present invention relates to a cumulatable ultra fine polymer particle consisting of one molecular chain of a polymer, a composite material comprising the aforesaid cumulatable ultra fine polymer particles cumulated on a substrate in a ratio of area occupied with the ultra fine polymer particles of at least 10%, and method of preparation thereof.
(2) Background Information
According to the solution theory of polymers, the polymer exists in a dilute solution as isolated chains. The dilute solution is the solution having a concentration of not more than C* defined by the following formula. EQU C*=3M/(4.pi.N.sub.A &lt;S.sup.2 &gt;.sup.3/2)
where C* is the concentration, M is the molecular weight of the polymers, .pi. is the ratio of the circumference of a circle to its diameter, N.sub.A is the Avogadro number, and &lt;S.sup.2 &gt; is the square mean of the radius of gyration of the polymer chain.
It has been considered that an ultra fine polymer particle consisting of one molecular chain of the polymer can probably be obtained by removing the solvent while maintaining the dispersion state of the polymer in the dilute solution.
However, it is very difficult to remove the solvent from the dilute solution while maintaining the molecular dispersion. The removal of the solvent under the usual conditions of the solvent casting process causes an increase of the concentration of the solution, finally resulting in association of the polymer molecules. For this reason, it is impossible to obtain an ultra fine polymer particle consisting of one molecular chain of the polymer by ordinary methods.
Although many useful applications are expected, almost no attempt has recently been made to obtain an ultra fine polymer particle consisting of one molecular chain of the polymer, because of this difficulty. Previously, some attempts were made. For example, M. J. Richardson, Proc. Roy. Sec. (London), A279, 50 (1964) reported the method for producing the ultra fine particle consisting of one polymer chain by spraying the dilute solution of the polymer in the mixed solvent onto a carbon vacuum-evaporated film and vaporizing the solvent therefrom. In this method, more volatile good solvent for the polymer and less volatile poor solvent were used in combination as the mixed solvent. It was reported that the composition was shifted to the poor solvent side during the vaporizing process of the solvent and the polymer became highly compressed conformation then became the ultra fine polymer particle. It was further described that the polymer widely spread on the substrate and an ultra fine polymer particle was not formed, when the dilute solution of the polymer in the good solvent alone was sprayed.
The ultra fine polymer particle consisting of one molecular chain of the polymer, prepared by the spray method described above, has the following disadvantages.
In the first place, the ultra fine polymer particle rigidly adheres to the substrate, because the dilute solution is sprayed on the solid substrate. Consequently, the ultra fine polymer particle thus obtained can not be cumulated on another substrate.
Secondly, it is impossible substantially to increase the ratio of area occupied with the particles, because a large amount of the solution sprayed on the solid substrate for increasing a ratio of area occupied with the particles causes association of the polymer chains. For this reason, the widely applicable structures such as the structure having the particles more densely packed and the structure having the particles cumulated in multi layers can not be obtained.
Further, R. F. Boyer et al, J. Appl. Phys., 16, 621 (1945) reported the summary of the paper presented by Kropa et al at Electron Microscope Society Meeting, New York City, Jan. 11-15, 1944 as follows:
"More recently Kropa, Burton, and Barnes have investigated films of polystyrene cast onto a water surface from solution in organic solvents. These films exhibited at various points black nodules whose size was in agreement with that predicted by the viscosity molecular weight of the polymers, if one assumed that the material in these nodules had the same bulk density as polystyrene. However, the method did not appear to work for all specimens, but only on certain high molecular weight polymers prepared in a special manner."
In this report, however, the details of the technical procedure and the obtained result are not disclosed. Therefore, the detailed informations are unknown.